1. Field of the Invention
This invention relates to cavitating fluid jets, and more particularly, to a jet having a surge chamber or section for amplifying cavitation in the fluid flow and limiting coning of the jet. This surge chamber also provides automatic sheathing action on the cavitation to sustain the bubbles in the fluid stream.
2. Description of the Prior Art
The jetting of fluid under high pressures is used for such purposes as cleaning of surfaces or drilling. In some cases, the fluid is projected as a cavitating fluid jet in which a stream of the fluid, such as water, has vapor cavities formed therein. Cavitation is the formation, growth and collapse of the vapor filled cavities or bubbles in the liquid which occur at a level where the local pressure is reduced below the vapor pressure of the liquid. The fluid is projected against a solid surface such that the vapor cavities collapse at the point of impact with sufficient force to cause substantial damage or advantageous erosion. Thus, the surface of an object can be cleaned or machined. Typical cavitating fluid jets are shown in U.S. Pat. Nos. 3,528,704 and 3,713,699 to Johnson, Jr.
Cavitating fluid jets are used both in air and in liquids, such as below the surface of the water in a subsea oil platform cleaning application. When used under water, there are generally no problems, and the fluid stream remains fairly confined as it is projected from the nozzle to the object to be cleaned. However, when cavitating fluid jets are used in air, the cavitation bubbles on the edge of the fluid stream dissipate quickly as the fluid leaves the nozzle. This reduces the amount of collapsing cavities at the point of impact. The shock and destructive force of the cavitating fluid jet is thus reduced. The greater the distance between the nozzle and the point of collapse of the cavitation bubbles, the greater the effect the surrounding atmosphere has on the bubble collapse. This is sometimes referred to as venting of the cavitating fluid jet which can ultimately change the jet into just a stream of liquid drops in a gaseous medium, rather than a plurality of vapor cavities in a liquid medium.
Therefore, a need exists for a cavitating fluid jet which tends to minimize the effect of the dissipation of the cavitation bubbles in the atmosphere. The surge enhanced cavitation jet of the present invention provides a solution to this problem by including a surge chamber or section immediately downstream from the orifice or separating section, wherein the surge chamber acts to amplify the cavitation such that the cavitation bubbles stay with the fluid longer as the stream is discharged from the nozzle and to provide continuous sheathing action for retaining the vapor cavities.